Floor grinding machine

ABSTRACT

A floor grinding machine includes a supporting frame, a grinding unit attached to the supporting frame, and a drive unit connected to the grinding unit. The grinding unit includes an upper housing, a lower housing rotatably arranged in relation to the upper housing, and a planetary drive system connected to the drive unit. The upper housing includes a first side wall. The lower housing includes a bottom plate and a second side wall. One or more grinding disks adapted for holding a tool are rotatably attached to the bottom plate. The planetary drive system is arranged to rotate the lower housing and the one or more grinding disks. The first side wall at least partly overlaps the second side wall. A gap is formed in a radial direction between the first side wall and the second side wall, and a sealing element is arranged in the gap.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. National Stage of PCT/SE2019/050021 filed on Jan. 15, 2019, which claims priority to Swedish Application No. 1850052-0, filed Jan. 18, 2018, each of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a floor grinding machine, and in particular to a floor grinding machine that is adapted for grinding or polishing floor surfaces, where the floor grinding machine comprises a supporting frame, a grinding unit connected to the supporting frame, and a drive unit connected to the grinding unit.

BACKGROUND

Floor grinding machines are commonly used for grinding or polishing floor surfaces, for example when there is a need to even out the floor surface or if a floor structure needs to be renovated. The floor grinding machine will when grinding the floor provide an even and smooth structure to the floor surface and the floor surface may be further treated or glossed after the grinding process if desired. Different types of grinding tools may be attached to the floor grinding machine in order to meet the demands on a desired surface structure of the floor.

Floor grinding machines that especially are suitable for grinding or polishing floor surfaces of concrete, stone, and concrete-like or stone-like materials, such as for example terrazzo, concrete of different qualities, limestone, sandstone, marble, slate, or granite, are often designed with a supporting frame, a grinding unit attached to the supporting frame, and a drive unit connected to the grinding unit. The grinding unit may be equipped with a drive system, such as a planetary drive system arranged within a housing structure or grinding head. One or more grinding disks are rotatably attached to the housing structure and are arranged to rotate in relation to the housing structure. The housing structure is adapted to rotate in relation to the supporting frame of the floor grinding machine, and the grinding disks and the housing structure are driven by the drive system.

During the grinding process, particles, water or other contaminants from the surface structure will easily penetrate different parts of the floor grinding machine and these contaminants may have a negative impact on the wear of the machine and parts of the machine. Especially the drive system needs to be protected from the contaminants, and therefore the rotating housing structure or grinding head may be designed as a sealed rotating unit preventing the contaminants from entering the drive system housed within the housing structure. Floor grinding machines and the machine parts are often very heavy in construction, and floor grinding machines of this type often weigh up to 500 kg depending on the model and size of the machine, and certain models could even weigh more than 700 kg. The servicing process of the machine and the cleaning of machine parts may therefore be a complicated and time consuming operation, especially when the rotating housing structure or grinding head needs to be removed from the grinding machine, or if the housing structure needs to be disassembled and assembled for servicing the drive system.

While rotating housing structures or grinding heads as described above are commonly used, there is a need to provide an improved and simplified floor grinding machine structure that would simplify the processes of assembling, disassembling, cleaning and servicing of the floor grinding machine, also for heavier machine models.

SUMMARY

An object of the present disclosure is to provide a floor grinding machine where the previously mentioned problems are avoided. This object is at least partly achieved by the features of the independent claims. The dependent claims contain further developments of the floor grinding machine.

The disclosure concerns a floor grinding machine comprising a supporting frame, a grinding unit attached to the supporting frame, and a drive unit connected to the grinding unit. The grinding unit comprises an upper housing, a lower housing rotatably arranged in relation to the upper housing, and a planetary drive system connected to the drive unit, where the upper housing comprises a top plate and a first side wall projecting downwards from the top plate in an axial direction. The lower housing comprises a bottom plate and a second side wall, where one or more grinding disks adapted for holding a tool are rotatably attached to the bottom plate, where the planetary drive system is arranged to rotate the lower housing and the one or more grinding disks respectively. The first side wall is coaxially arranged in relation to the second side wall, and the first side wall is in the axial direction at least partly overlapping the second side wall. A gap is formed in a radial direction between the first side wall and the second side wall, and a sealing element is arranged in the gap.

A floor grinding machine having a grinding unit with this configuration is providing a simple design of the grinding unit with a tight and sealed grinding unit construction preventing particles, water or other contaminants from the surface structure to penetrate different parts of the grinding unit. This will prevent that the contaminants are having a negative impact on the wear of the machine and parts of the machine. Also, the maintenance and servicing process of the machine as well as the cleaning process of the machine and machine parts can be made much more fast and convenient for the service personnel, since with this construction of the grinding unit, the disassembling and assembling of the grinding unit is possible to make much more efficient. Further, with this construction, an improved and simplified floor grinding machine structure is achieved that simplifies the processes of assembling, disassembling, cleaning and servicing the floor grinding machine, also for heavier machine models.

According to an aspect of the disclosure, the gap is formed in the radial direction between an inner surface of the first side wall and an outer surface of the second side wall. The gap is in this way forming a suitable area for the sealing element, where the sealing element is forming a tight seal between the upper housing and the lower housing. The lower housing can with this construction efficiently rotate in relation to the upper housing without major frictional forces.

According to another aspect of the disclosure, the second side wall is projecting upwards and/or downwards from the bottom plate in the axial direction, and the gap is formed in the radial direction between an inner surface of the first side wall and an outer surface of the second side wall. With this configuration, the sealing element can be efficiently arranged between the side walls providing a tight seal between the upper housing and the lower housing.

According to another aspect of the disclosure, the sealing element is arranged along peripheries of the inner surface and the outer surface respectively, and an outer edge of the sealing element is attached to the inner surface of the first side wall, wherein the outer surface of the second side wall is slidably in contact with an inner edge of the sealing element. The sealing element is attached to the upper housing and when the lower housing is rotating in relation to the upper housing the sealing element is sliding against the lower housing and is establishing a tight seal between the side walls.

According to a further aspect of the disclosure, the sealing element is releasably attached to the inner surface of the first side wall, and arranged to be adjustably positioned in the axial direction along the inner surface of the first side wall. A repositioning of the sealing element may be desired if the part of the outer surface of the lower housing that is sliding against the sealing element becomes worn. Through the repositioning of the sealing element in the axial direction a tight seal between the upper housing and the lower housing can be maintained even if a part of the outer surface of the lower housing is worn.

According to another aspect of the disclosure, the inner surface of the first side wall has an essentially circular cross-sectional shape around an axis extending in the axial direction and the outer surface of the second side wall has an essentially circular cross-sectional shape around the axis extending in the axial direction. With this geometry, the gap is ring-shaped or has an annular shape so that the sealing element can be made with a simple and efficient sealing construction.

According to another aspect of the disclosure, the top plate and the first side wall of the upper housing are forming a first space, where the lower housing at least partly is arranged inside the first space of the upper housing. Since the lower housing at least partly is arranged inside the first space a compact grinding unit is achieved.

According to a further aspect of the disclosure, the second side wall is projecting upwards from the bottom plate in the axial direction, and where the gap is formed in the radial direction between an inner surface of the second side wall and an outer surface of the first side wall. With this configuration, the sealing element can in another embodiment be efficiently arranged between the side walls providing a tight seal between the upper housing and the lower housing.

According to a further aspect of the disclosure, the inner surface of the second side wall has an essentially circular cross-sectional shape around an axis extending in the axial direction and the outer surface of the first side wall has an essentially circular cross-sectional shape around the axis extending in the axial direction. Also, with this configuration, the gap is ring-shaped or has an annular shape so that the sealing element can be made with a simple and efficient sealing construction.

According to a further aspect of the disclosure, the bottom plate and the second side wall of the lower housing are forming a second space, where the upper housing at least partly is arranged inside the second space of the lower housing. Since the upper housing at least partly is arranged inside the second space a compact grinding unit is achieved.

According to a further aspect of the disclosure, the upper housing, the lower housing, and the sealing element are forming a sealed volume of the grinding unit, where the sealing element is preventing contaminants from entering the sealed volume. In this way the rotating lower housing is not designed in a traditional way as a sealed rotating unit. Instead, the rotating lower housing has an open structure and the contaminants are prevented from entering the drive system housed within the grinding unit through the configuration with the sealed volume established by the upper housing, the sealing element and the rotating lower housing. This structure is providing a grinding unit adapted for easy maintenance and service. The lower housing has an open structural configuration upwards in the axial direction. This means that the rotating lower housing is not covered with a lid or similar covering structure that is rotating with the lower housing. In this way the rotating lower housing is designed in a more simple and convenient open structured way that makes maintenance and servicing processes of the machine as well as the cleaning process of the machine and machine parts much faster and more convenient for service personnel.

According to another aspect of the disclosure, a drive shaft of the planetary drive system is releasably connected to the drive unit via a drive coupling, and where the drive shaft is passing through an opening in the upper housing. With this arrangement, the lower housing can be removed from the grinding unit structure in a fast and convenient way.

According to a further aspect of the disclosure, the planetary drive system comprises a belt drive unit arranged on the lower housing connected to the drive unit, where the belt drive unit is arranged to rotate the lower housing in relation to the upper housing, and to rotate the one or more grinding disks in relation to the lower housing. The planetary drive system is providing a simple, reliable and efficient driving of the grinding unit through the belt drive unit. The drive system can be made in a compact format suitable for being arranged on the lower housing structure so that the drive system is arranged inside the grinding unit, where it is prevented from coming into contact with water, particles or other contaminants.

According to other aspects of the disclosure, the belt drive unit comprises a drive belt, where each of the one or more grinding disks is connected to a pulley, where a rotational movement is transferred from the drive unit to the one or more grinding disks via the drive belt and the one or more pulleys. Further, the planetary drive system comprises a ring gear arranged on the inner surface of the upper housing, where the ring gear is interacting with at least one pinion rotatably connected to the lower housing, and where the at least one pinion is rotated by the belt drive unit. These features provide a simple, reliable and efficient construction of the planetary drive system.

According to other aspects of the disclosure, the grinding unit is pivotally attached to the supporting frame about a lateral axis, and further the upper housing is non-rotatably arranged in relation to the supporting frame, which is providing a flexible and stable construction of the grinding machine.

According to another aspect of the disclosure, the upper housing and/or the lower housing are made of ductile cast iron. Ductile cast iron will provide a strong and heavy construction to the upper and lower housings, and the design of the housings can be precision made through a die casting process.

According to a further aspect of the disclosure, the sealing element is a radial seal having a continuous configuration made of an elastomeric material, such as nitrile butadiene rubber (NBR) or carboxylated nitrile rubber (XNBR). The use of a continuous configuration, where the sealing element can be made of a single piece of material in an elastomeric material will provide a tight seal between the upper housing and the lower housing.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will be described in greater detail in the following, with reference to the attached drawings, in which

FIG. 1a shows schematically, in a perspective view from above a floor grinding machine according to the disclosure,

FIG. 1b shows schematically, in a side view a floor grinding machine according to the disclosure,

FIG. 1c shows schematically, in view from below a floor grinding machine according to the disclosure,

FIG. 2a-b show schematically, in perspective views a grinding unit and a cross-section of the grinding unit of the floor grinding machine according to the disclosure

FIG. 2c-d show schematically, in perspective views cross-sections of a part of the grinding unit according to the disclosure, with alternative embodiments of a sealing element,

FIG. 3 shows schematically, in a side view a cross-section of the grinding unit according to the disclosure,

FIG. 4a-b show schematically, in a perspective view from above and a view from above a lower housing and a planetary drive system of the grinding unit according to the disclosure, and

FIG. 5a-c show schematically, inside view cross-sections of the grinding unit according to different embodiments of the disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Various aspects of the disclosure will hereinafter be described in conjunction with the appended drawings to illustrate and not to limit the disclosure, wherein like designations denote like elements, and variations of the described aspects are not restricted to the specifically shown embodiments, but are applicable on other variations of the disclosure.

In FIGS. 1a -c, a floor grinding machine 1 that is used for grinding or polishing floor surfaces is schematically shown. Floor grinding machines are suitable for example when there is a need to even out floor surfaces or if a floor structure needs to be renovated. The grinding machine 1 will during operation grind the floor surface into a desired surface structure, and the grinding operation may be optimized for a certain floor surface material by using specific grinding tools suitable for the specific floor surface material. The floor surface may be further treated or glossed, and different types of grinding or polishing tools may be attached to the floor grinding machine 1 in order to meet the demands on a desired floor surface structure. The grinding machine 1 may be used for grinding or polishing floor surfaces of concrete, stone, and concrete-like or stone-like materials, such as for example terrazzo, concrete of different qualities, limestone, sandstone, marble, slate, or granite.

The floor grinding machine 1 comprises a supporting frame 2 designed as a conventional frame structure for holding other components of the grinding machine 1. The supporting frame 2 is for example made of steel or other suitable materials such as aluminum, composite materials or a combination of different materials. The supporting frame 2 may be provided with a pair of rear wheels 31 arranged in a rear part of the floor grinding machine, and one or more front wheels 32 arranged in a front part of the floor grinding machine 1, where the wheels may be attached to the supporting frame 2 in a suitable conventional way. The floor grinding machine 1 may be manually pushed during the grinding operation or alternatively driven by a drive system arranged to drive one or more of the wheels. A handle 33 may also be attached to the supporting frame 2 in a rear part of the floor grinding machine 1, and the handle 33 is used for pushing, pulling or maneuvering the floor grinding machine 1 in different directions. The handle 33 may be arranged so that it can be pivoted in different positions. The grinding machine 1 may as an alternative be driven by an automated drive system that is enabling a stable and smooth grinding function. A radio controlled system can be used for controlling the motion and grinding speed of the floor grinding machine 1, and a remote control may be connected to the drive system to allow an operator to move the machine in any desired direction. In this way the floor grinding machine 1 can be maneuvered with high precision for example in tight areas.

The rear wheels 31 may be arranged so that they are displaceable in a longitudinal direction LO in relation the supporting frame 2. The rear wheels 31 may be suspended on rear wheel shafts 36 extending in a lateral direction LA in relation to the supporting frame 2 in a way so that they can be adjusted in different positions in the longitudinal direction LO. In this way the center of gravity of the floor grinding machine can be shifted forwards and backwards in order to provide a suitable grinding pressure on the floor structure during the grinding operation. The more rearward the rear wheels 31 are positioned in relation to the supporting frame 2 in the longitudinal direction LO, the more the pressure on the front part of the grinding machine will increase. The rear wheels 31 may be driven by a suitable driving mechanism, and as an option they may be individually driven so that a direction of travel of the machine may be controlled.

As shown in FIGS. 1a -c, the floor grinding machine is provided with a front wheel structure with one front wheel 32, which is held in position in relation to the supporting frame 2 with a front wheel bracket 37. The front wheel 32 may be arranged as a swivel wheel or caster for easy maneuvering of the floor grinding machine 1 during transport or grinding. The front wheel 32 may be detachable from the frame structure 2 so that during the grinding process, the floor grinding machine 1 can be operated without the front wheel 32 if desired. As an alternative the front wheel 32 and the front wheel bracket 37 holding the front wheel 32 may be arranged so that the front wheel structure can be pivoted in different positions about a front wheel bracket axis 38 extending in the lateral direction LA. In this way, the front wheel structure may be pivoted so that the front wheel 32 is not in contact with the floor during the grinding operation, or alternatively the front wheel structure is held in a position in relation to the floor structure where the front wheel 32 is in contact with the floor so that a desired grinding pressure is achieved during the grinding operation. The front wheel structure may also be designed so that the grinding pressure can be controlled and adjusted during the grinding operation through pivoting the front wheel bracket 37 in relation to the frame structure 2. In this way, when the front wheel 32 is adjusted in a direction downwards so that the front part of the supporting frame 2 is moved upwards from the floor surface, the grinding pressure will decrease, and when the front wheel 32 is adjusted in a direction upwards, the grinding pressure will increase.

As further shown in FIGS. 1a and 1 b, a housing unit 34 is attached to the frame structure 2. The housing unit 34 may for example comprise an electronic or computerized control system of the floor grinding machine 1 with associated controls and displays. The housing unit 34 may further comprise a water tank and necessary electrical components and connections.

A grinding unit 3 is attached to the supporting frame 2, and positioned in front of the rear wheels 31. The grinding unit 3 is arranged for grinding or polishing the floor surface when the floor grinding machine 1 moves along the floor and the grinding unit 3 is providing an even and smooth structure to the floor surface when the floor grinding machine is being operated. The grinding unit 3 may be pivotally attached to or suspended in relation to the supporting frame 2 so that the grinding unit 3 will have a position that is essentially parallel to the floor surface during the grinding operation. The grinding unit 3 may for example be attached to the frame structure 2 with bolts 35 or similar arrangements so that the grinding unit 3 can be pivoted around a lateral axis L, as shown in FIG. 1 a. The lateral axis L is extending in the lateral direction LA in relation to the supporting frame 2 of the grinding machine 1, as indicated in FIG. 1 a. In this way, the grinding machine 1 may typically be supported by its grinding unit 3 during the grinding operation. Thus, the grinding machine 1 may have a construction where the grinding unit 3 is pivotally attached to the supporting frame 2 about the lateral axis L.

A drive unit 4 is as shown in FIGS. 1a and 1b connected to the grinding unit 3. The drive unit 4 may be of any conventional type, such as for example an electric motor or an internal combustion engine. The internal combustion engine may be gas driven, where a suitable gas for example may be propane. As an alternative, two or more electric motors or combustion engines may be used as the drive unit 4 instead of a single motor or engine unit, depending on the construction and design of the floor grinding machine 1.

As shown in FIGS. 2b , 3 and 5 a-c, the grinding unit 3 comprises an upper housing 5 and a lower housing 6, and the lower housing 6 is rotatably arranged in relation to the upper housing 5. As shown for example in FIGS. 2b and 5a -c, the lower housing 6 is arranged so that the lower housing 6 rotates about an axis A extending in an axial direction AX of the grinding unit 3 during the grinding operation. The upper housing 5 is non-rotatably arranged in relation to the supporting frame 2. In this way the upper housing 5 is arranged so that it is not rotating about the axis A extending in the axial direction AX of the grinding unit 3 during the grinding operation. However, as described above, the grinding unit 3 may pivot about the lateral axis L in relation to the supporting frame 2. As further shown in the figures, a radial direction R of the grinding unit 3 is defined as a direction which is perpendicular to or essentially perpendicular to the axial direction AX of the grinding unit 3. The grinding unit 3 as such has an extension both in the axial direction AX and in the radial direction R as will be further described.

The grinding unit 3 further comprises a planetary drive system 7, which is connected to the drive unit 4. The planetary drive system 7 may be a conventional planetary drive system used for floor grinding machines. During operation of the grinding machine, the drive unit 4 is connected to the planetary drive system 7 so that a rotary motion of the drive unit 4 is transferred to the planetary drive system 7. The planetary drive system 7 is arranged to rotate the lower housing 6 in relation to the upper housing 5, as will be further described below. The drive unit 4 may be provided with an outgoing shaft that is operably connected to the planetary drive system 7 of the grinding unit 3. The outgoing shaft of the drive unit 4 may be directly connected to a drive shaft 20 of the planetary drive system 7 or indirectly connected to the drive shaft 20 via a gear unit, depending on the construction of the floor grinding machine. As shown in the figures, the drive shaft 20 of the planetary drive system 7 is extending essentially in the axial direction AX and the drive shaft 20 is arranged to rotate about the axis A. The drive unit 4 may be attached to the upper housing 5 of the grinding unit 3 with screws, bolts or other suitable fastening means.

The upper housing 5 comprises a top plate 8 and a first side wall 9, as shown in FIGS. 2b , 3 and 5 a-c. The first side wall 9 is projecting in a direction downwards from the top plate 8 in the axial direction AX of the grinding unit 3. The top plate 8 may, as shown in FIGS. 5a -c, have a flat cross-sectional configuration or shape when viewed from the side. However other suitable cross-sectional configurations or shapes are also possible, such as for example curved or stepped. In FIG. 2b , a stepped configuration of the top plate 8 is shown more in detail. The top plate 8 as well as the upper housing 5 may have an essentially circular configuration when viewed from above or below and the top plate 8 may be provided with an outer flange 39, as shown in FIGS. 2a and 2b , to which the drive unit 4 is attached.

The first side wall 9 may extend essentially from and around the outer periphery of the top plate 8, and the first side wall 9 may be formed into a suitable shape. As shown in FIGS. 5a -c, the first side wall 9 may have an essentially straight cross-sectional shape when viewed from the side. As an alternative, the first side wall 9 may instead have a curved or stepped cross-sectional shape, and in FIG. 2b the first side wall 9 is having a stepped cross-sectional shape. The first side wall 9 has an inner surface 16 a and an outer surface 16 b.

The top plate 8 and the first side wall 9 may be arranged as an integrated structure that is forming the upper housing 5, and the upper housing 5 may be made of one single piece of material, or alternatively in two or more parts that are assembled into an integrated structure. A suitable material for the upper housing 5 is for example ductile cast iron. An upper housing 5 made of ductile cast iron will provide a strong and heavy construction, and the design of the upper housing 5 can be precision made through a suitable die casting process. Alternatively, the upper housing 5 may be made of other materials, such as for example steel, aluminum or other metals, plastic or composite materials as well as combinations of different materials, which material or materials are shaped into a desired housing structure.

The lower housing 6 comprises a bottom plate 11 and a second side wall 12. In the embodiment shown in FIGS. 2b -d, 3 and 4 a-b, the second side wall 12 may extend or project in a direction downwards from the bottom plate 11 in the axial direction AX of the grinding unit 3. The second side wall 12 extends essentially from and around the outer periphery of the bottom plate 11. The side wall 12 may also as an alternative extend both upwards and downwards from the bottom plate 11 in the axial direction AX of the grinding unit 3. In the embodiment shown in FIGS. 2b -d, 3 and 4 a-b, wall sections 45 are extending in a direction upwards from the bottom plate 11.

As shown in the embodiments in FIGS. 5a and 5c , the second side wall 12 may extend or project in a direction upwards from the bottom plate 11 in the axial direction AX of the grinding unit 3. In this way, the second side wall 12 extends essentially from and around the outer periphery of the bottom plate 11. In an alternative embodiment, as shown in FIG. 5b , the lower housing 6 is formed by the bottom plate 11, and the second side wall 12 is in this embodiment formed by the side edges of the bottom plate 11, where the second side wall 12 thus extends around the outer periphery of the bottom plate 11 and is having a dimension in the axial direction AX of the grinding unit 3 corresponding to the thickness of the outer part of the bottom plate 11.

The bottom plate 11 may, as shown in FIGS. 5a -c, have a flat cross-sectional configuration or shape when viewed from the side. However other suitable cross-sectional configurations or shapes are also possible, such as for example curved or stepped. In for example FIG. 2b , a stepped bottom plate 11 is shown. The bottom plate 11 and also the lower housing 6 may have an essentially circular configuration when viewed from above or below.

The second side wall 12 may be formed into a suitable shape depending on the design of the grinding unit 3. As shown in FIGS. 5a -c, the second side wall 12 may have an essentially straight cross-sectional shape when viewed from the side. As an alternative, the second side wall 12 may instead have other suitable shapes, such as for example a curved or stepped cross-sectional shape. In FIGS. 2b-d a part of the second side wall 12 is having an essentially straight cross-sectional shape arranged in the axial direction AX of the grinding unit 3, and the second side wall 12 is provided with a radially outwards and downwards projecting edge part 40. In the embodiments shown in FIGS. 2b , 3, 5 a and 5 c, the second side wall 12 has an inner surface 17 a and an outer surface 17 b. In the embodiment shown in FIG. 5b , the second side wall has an outer surface 17 b.

The bottom plate 11 and the second side wall 12 may be arranged as an integrated structure that is forming the lower housing 6, and the lower housing 6 may be made of one single piece of material, or alternatively in two or more parts that are assembled into an integrated structure. A suitable material for the lower housing 6 is for example ductile cast iron. A lower housing 6 made of ductile cast iron will provide a strong and heavy construction, and the design of the lower housing 6 can be precision made through a suitable die casting process. Alternatively, the lower housing 6 may be made of other materials, such as for example steel, aluminum or other metals, plastic or composite materials as well as combinations of different materials, which material or materials are shaped into a structure suitable for the lower housing 6.

If a heavy construction of the grinding unit 3 is desired, the upper housing 5 and/or the lower housing 6 may be made of ductile cast iron. A heavy construction of the grinding unit 3 will provide an efficient grinding of the floor surface if using suitable grinding tools 14.

One or more grinding disks 13 adapted for holding one or more grinding tools 14 are rotatably attached to the bottom plate 11 of the lower housing 6. The grinding disks 13 may be rotatably attached to the bottom plate 11 in a conventional way, for example by using suitable bearings. Each of the grinding disks 13 may be attached to the lower part of a disk shaft 41 extending through the bottom plate 11 in the axial direction AX of the grinding unit 3, and the disk shafts 41 may be arranged for rotating the grinding disks 13. The lower housing 6 may rotate in a clockwise or a counter-clockwise direction in relation to the upper housing 5 and the grinding disks 13 may be arranged so that they can rotate in the opposite rotational direction to achieve a desired result when grinding the floor structure. Alternatively, the lower housing 6 and the grinding disks 13 may rotate in the same direction. In the embodiments shown in the figures, the grinding unit 3 has three grinding disks 13 rotatably attached to the bottom plate 11. However, the number of grinding disks may be varied depending on the design of the grinding machine 1. The grinding disks 13 may be provided with suitable holders for the tools 4 so that the tools 14 easily can be attached to and removed from the grinding disks.

The planetary drive system 7 is arranged to rotate the lower housing 6 and the one or more grinding disks 13 respectively, where the lower housing is rotated by the planetary drive system 7 in relation to the upper housing 5 and the grinding disks 13 are rotated by the planetary drive system 7 in relation to the lower housing 6. The planetary drive system 7 may be of any conventional type used for floor grinding machines, and a suitable drive system for the floor grinding machine 1 will be further described below.

The tools 14 may be in the form of plates with bonded abrasives, where the abrasives are in the form of a three-dimensional body comprising abrasive particles and a matrix material. The material may for example be a polymer material or a metallic material. As an alternative, the tools 14 may be in the form of cutting elements that for example are suitable for removal of glue, paint, lacquer or other surface treatment compounds from the floor surface. During the grinding operation, the grinding unit 3 with the tools 14 will exert a certain pressure on the floor, and as described above, the grinding pressure can be adjusted by adjusting the rear wheels 31 and/or the front wheel 32. Different parameters can be programmed in the grinding machine system in order to achieve a desired result when grinding the floor surface. Examples of parameters that can be varied is for example the rotational speed of the lower housing 6, the rotational speed of the grinding disks 13, the forward speed of the grinding machine and the pressure exerted by the tools 14 on the floor surface. The grinding machine system may be programmed so that the system recommends the right type of parameters for a specific type of floor surface.

The grinding unit 3 may be designed with a configuration, as indicated in FIGS. 2b , 3 and 5 a-c, so that the first side wall 9 is coaxially arranged in relation to the second side wall 12, and further so that the first side wall 9 in the axial direction AX at least partly is overlapping the second side wall 12. The upper housing 5 and the lower housing 6 may thus be positioned in an overlapping manner in relation to each other in the axial direction AX so that the first side wall 9 is coaxially arranged in relation to the second side wall 12 about the axis A extending in the axial direction AX of the grinding unit 3. In this way a gap 15 is formed in a radial direction R of the grinding unit 3 between the first side wall 9 and the second side wall 12, and as shown in the figures, the gap 15 is formed in the overlapping region between the first side wall 9 and the second side wall 12, where the side walls are having different diameters. When viewed from below or above, the gap 15 is ring-shaped or has an annular cross-sectional shape around the axis A that extends between the first side wall 9 and the second side wall 12.

In FIGS. 2b -d, 3, 4 a-b an embodiment of the grinding unit 3 is shown, where the second side wall 12 is projecting in a direction downwards from the bottom plate 11 in the axial direction AX. In FIG. 5a , an embodiment of the grinding machine 1 is shown, where the second side wall 12 is projecting in a direction upwards from the bottom plate 11 in the axial direction AX. In FIG. 5a , the grinding unit 3 is only schematically shown in a cross-sectional view without the grinding disks 13 to better illustrate the position of the upper housing 5 in relation to the lower housing 6. In these embodiments, the upper housing 5 is arranged in relation to the lower housing 6 so that the first side wall 9 is coaxially arranged in relation to the second side wall 12. The first side wall 9 is in the axial direction AX partly overlapping the second side wall 12. The gap 15 is formed in the radial direction R between the inner surface 16 a of the first side wall 9 and the outer surface 17 b of the second side wall 12. The inner surface 16 a of the first side wall 9 has an essentially circular cross-sectional shape around the axis A and the outer surface 17 b of the second side wall 12 has an essentially circular cross-sectional shape around the axis A, and in this way the lower housing 6 can rotate in relation to the upper housing 5 with an essentially constant gap 15 in the radial direction R and with an essentially constant overlap in the axial direction AX. The top plate 8 and the first side wall 9 of the upper housing 5 are forming a first space 10, and due to the overlapping relationship between the upper housing 5 and the lower housing 6 in the axial direction AX the lower housing 6 is at least partly arranged inside the first space 10 of the upper housing 5.

In FIG. 5b , another embodiment of the grinding machine 1 is shown, where the lower housing 6 is formed by the bottom plate 11, and the second side wall 12 is in this embodiment formed by the side edges of the bottom plate 11. The second side wall 12 thus extends around the outer periphery of the bottom plate 11 and is having a dimension in the axial direction AX of the grinding unit 3 corresponding to the thickness of the outer part of the bottom plate 11. The upper housing 5 is arranged in relation to the lower housing 6 so that the first side wall 9 is coaxially arranged in relation to the second side wall 12. The first side wall 9 is in the axial direction AX overlapping the second side wall 12. In this embodiment, the gap 15 is formed in the radial direction R between the inner surface 16 a of the first side wall 9 and the outer surface 17 b of the second side wall 12. In FIG. 5b , the grinding unit 3 is only schematically shown in a cross-sectional view without the grinding disks to better illustrate the position of the upper housing 5 in relation to the lower housing 6. The inner surface 16 a of the first side wall 9 has an essentially circular cross-sectional shape around the axis A and the outer surface 17 b of the second side wall 12 has an essentially circular cross-sectional shape around the axis A, and in this way the lower housing 6 can rotate in relation to the upper housing 5 with an essentially constant gap 15 in the radial direction R and with an essentially constant overlap in the axial direction AX. As shown in FIG. 5b , the top plate 8 and the first side wall 9 of the upper housing 5 are forming a first space 10, and due to the overlapping relationship between the upper housing 5 and the lower housing 6 in the axial direction AX the lower housing 6 is at least partly arranged inside the first space 10 of the upper housing 5.

In FIG. 5c , a further embodiment of the grinding machine 1 is shown, where the second side wall 12 is projecting in a direction upwards from the bottom plate 11 in the axial direction AX. The upper housing 5 is arranged in relation to the lower housing 6 so that the first side wall 9 is coaxially arranged in relation to the second side wall 12. The first side wall 9 is in the axial direction AX partly overlapping the second side wall 12. In this embodiment, the gap 15 is formed in the radial direction R between an inner surface 17 a of the second side wall 12 and an outer surface 16 b of the first side wall 9. In FIG. 5c , the grinding unit 3 is only schematically shown in a cross-sectional view without the grinding disks to better illustrate the position of the upper housing 5 in relation to the lower housing 6. The inner surface 17 a of the second side wall 12 has an essentially circular cross-sectional shape around the axis A and the outer surface 16 b of the first side wall 9 has an essentially circular cross-sectional shape around the axis A, and in this way the lower housing 6 can rotate in relation to the upper housing 5 with an essentially constant gap 15 in the radial direction R and with an essentially constant overlap in the axial direction AX. As shown in FIG. 5c , the bottom plate 11 and the second side wall 12 of the lower housing 6 are forming a second space 19, and due to the overlapping relationship between the upper housing 5 and the lower housing 6 in the axial direction AX the upper housing 5 is at least partly arranged inside the second space 19 of the lower housing 6.

In the different embodiments of the grinding machine 1, a sealing element 18 is arranged in the gap 15. The sealing element 18 may be designed as a continuous sealing unit or element made of one single piece of material that is covering the gap 15 and is used for preventing particles, water or other contaminants that are coming from the floor surface during the grinding operation from penetrating the interior structure of the grinding unit 3, since these contaminants may have a negative impact on the wear of the grinding unit 3 and parts of the grinding unit 3. Especially the planetary drive system 7 arranged inside the grinding unit 3 needs to be protected from the contaminants, and therefore the rotating lower housing 6 is sealed with the sealing element 18 in relation to the upper housing 5. In this way, the contaminants are prevented from entering the planetary drive system 7 housed within the grinding unit 3. As an alternative, the sealing element 18 may be instead built up of two or more pieces of material forming a sealing structure that is arranged in the gap 15.

Through the use of the sealing element 18 arranged in the gap 15 between the upper housing 5 and the rotating lower housing 6, the grinding unit 3 can be designed in a way where the interior structure of the grinding unit 3 is easily accessible during service or maintenance of the grinding machine 1. Since the floor grinding machine 1 and the machine parts are heavy in construction, it is desirable that the servicing process and the cleaning of the machine parts can be achieved in a simple and fast operation. Through the construction of the grinding unit 3 described above, the grinding unit 3 may be designed so that it is easily disassembled and assembled, and the lower housing 6 can be arranged so that it is easily removed from the upper housing 5, for example when there is a need for servicing the grinding machine 1 or the drive system. Thus, through the construction of the grinding unit 3 a simplified floor grinding machine structure that makes the processes of assembling, disassembling, cleaning and servicing of the floor grinding machine 1 can be achieved.

In the embodiments shown in FIGS. 2b -d, 3, 5 a-b, the sealing element 18 is arranged in the gap 15 along the periphery of the inner surface 16 a of the first side wall 9 and along the periphery of the outer surface 17 b of the second side wall 12. An outer edge 23 of the sealing element 18 is attached to the inner surface 16 a of the first side wall 9, with for example glue or other suitable fastening means. The sealing element 18 may be arranged as a radial seal having a shape and dimension so that the outer edge 23 snugly fits the periphery of the inner surface 16 a of the first side wall 9, and through this arrangement the sealing element 18 is held in place in relation to the inner surface 16 a of the first side wall 9 with frictional forces. Radial seals are used between rotating and stationary machine components or between two components in relative motion. The sealing element 18 may be attached to the first side wall 9 for example through press fitting. When viewed from above or below, the sealing element 18 has a continuous configuration and is ring-shaped or has an annular shape that fits the shape of the gap 15 between the first side wall 9 and the second side wall 12. The outer surface 17 b of the second side wall 12 is slidably in contact with an inner edge 24 of the sealing element 18. When the lower housing 6 is rotating in relation to the upper housing 5, the outer edge 23 of the sealing element is attached to the inner surface 16 a of the first side wall 9 and the outer surface 17 b of the second side wall 12 is sliding against the inner edge 24 of the sealing element 18. In this way a tight seal is established between the upper housing 5 and the rotating lower housing 6 preventing contaminants from entering the interior structure of the grinding unit 3. The sealing element 18 may be shaped or profiled in different ways depending on the design of the grinding unit 3, as shown in FIGS. 2c -d. As shown in FIGS. 2c -d, the sealing element may have a cross-sectional configuration that is U-shaped or L-shaped, where the sealing element 18 is forming a radial seal having a sealing lip, where the inner edge 24 of the sealing element 18 is forming the sealing lip. The sealing lip is for example made of an elastomeric or thermoplastic material. The edge of the sealing lip that is in contact with the second side wall 12 may be formed by molding, cutting or grinding, and the sealing element 18 is in this way arranged so that the inner edge 24 is pressed against the outer surface 17 b of the second side wall 12. The sealing element 18 may also be arranged with two or more sealing lips if desired. As an alternative two or more co-operating sealing elements 18 may be used in combination, depending on the design of the grinding unit 3. Further, the sealing element 18 may be reinforced with steel or other suitable materials and provided with a spring element, such as a garter spring providing radial load, if needed. In an alternative embodiment, the inner surface 24 of the sealing element 18 may instead be attached to the outer surface 17 b of the second side wall 12 and the inner surface 16 a of the first side wall 9 is slidably in contact with the outer edge 23 of the sealing element 18. In this alternative embodiment the outer edge 23 may be formed with one or more sealing lips as described above. The sealing element 18 may be made of any suitable material, such as for example an elastomeric or thermoplastic material. Examples of materials that may be used are rubber materials, such as natural rubber or synthetic rubber, and polyurethane. Examples of suitable synthetic rubber materials providing good sealing properties are nitrile rubber, such as nitrile butadiene rubber (NBR) and carboxylated nitrile rubber (XNBR).

In the embodiment shown in FIG. 5c , the sealing element 18 is arranged in the gap 15 along the periphery of the inner surface 17 a of the second side wall 12 and along the periphery of the outer surface 16 b of the first side wall 9. The outer edge 23 of the sealing element 18 may be attached to the inner surface 17 a of the second side wall 12, with for example glue or other suitable fastening means as described in the embodiments above, and may also be arranged as a radial seal having a shape and dimension so that the outer edge 23 snugly fits the periphery of the inner surface 17 a of the second side wall 12, and through this arrangement the sealing element 18 is held in place in relation to the inner surface 17 a of the second side wall 12 with frictional forces. The outer surface 16 b of the first side wall 9 is slidably in contact with the inner edge 24 of the sealing element 18. When the lower housing 6 is rotating in relation to the upper housing 5, the outer edge 23 of the sealing element is attached to the inner surface 17 a of the second side wall 12 and the outer surface 16 b of the first side wall 9 is sliding against the inner edge 24 of the sealing element 18. In this way a tight seal is established between the upper housing 5 and the rotating lower housing 6 preventing contaminants from entering the interior structure of the grinding unit 3. As an alternative, the inner surface 24 of the sealing element 18 may instead be attached to the outer surface 16 b of the first side wall 9 and the inner surface 17 a of the second side wall 12 is slidably in contact with the outer edge 23 of the sealing element 18. Also, in this embodiment, when viewed from above or below, the sealing element 18 has a continuous configuration and is ring-shaped or has an annular shape that fits the shape of the gap 15 between the first side wall 9 and the second side wall 12. The sealing element 18 may be of the types and constructions described in relation to the embodiments above.

In the embodiments shown in FIGS. 2b -d, 3 and 5 a-b, the sealing element 18 may be releasably attached to the inner surface 16 a of the first side wall 9, and arranged to be adjustably positioned in the axial direction LA along the inner surface 16 a of the first side wall 9. In this way the sealing element may be removed and replaced with a new seal if needed, or alternatively be repositioned or adjusted in the axial direction AX in relation to the rotating lower housing 6. A repositioning of the sealing element 18 may be desired if the part of the outer surface 17 b of the lower housing 6 that is sliding against the inner edge 24 of the sealing element 18 becomes worn. Through the repositioning of the sealing element 18 in the axial direction AX a tight seal between the upper housing 5 and the lower housing 6 can be maintained even if a part of the outer surface 17 b of the lower housing 6 is worn. As an alternative for the embodiments shown in FIGS. 2b -d, 3 and 5 a, the sealing element may instead be releasably attached to the outer surface 17 b of the second side wall 12 and arranged to be adjustably positioned in the axial direction LA along the outer surface 17 b of the second side wall 12.

Also, in the embodiment shown in FIG. 5c the sealing element 18 may be releasably attached to the inner surface 17 a of the second side wall 12 and arranged to be adjustably positioned in the axial direction LA along the inner surface 17 a of the second side wall 12. In this way the sealing element may be removed and replaced with a new seal if needed, or alternatively be repositioned or adjusted in the axial direction AX in relation to the rotating lower housing 6. As an alternative for the embodiment shown in FIG. 5c , the sealing element may instead be releasably attached to the outer surface 16 b of the first side wall 9 and arranged to be adjustably positioned in the axial direction LA along the outer surface 16 b of the first side wall 9.

In the different embodiments described, the upper housing 5, the lower housing 6, and the sealing element 18 are forming a sealed volume 22 of the grinding unit 3 and the sealing element 18 is preventing contaminants from entering the sealed volume 22. The planetary drive system 7 or parts of the planetary drive system 7 arranged within the sealed volume 22 is thus protected from the contaminants. As further shown, the lower housing 6 has an open structural configuration upwards in the axial direction LA. This means that the rotating lower housing 6 is not covered with a lid or similar covering structure that is rotating with the lower housing 6. In this way the rotating lower housing 6 is not designed in a traditional way as a sealed rotating unit. Instead, the rotating lower housing 6 has an open structure and the contaminants are prevented from entering the drive system housed within the grinding unit 3 through the configuration with the sealed volume 22 established by the non-rotating upper housing 5, the sealing element 18 and the rotating lower housing 6. This structure is providing a grinding unit 3 adapted for easy maintenance or service. A traditional sealed rotating unit is complex and heavy to disassemble and assemble during service and maintenance.

To achieve a grinding unit 3 that is easy to assemble and disassemble, the planetary drive system 7 is releasably connected to the outgoing shaft of the drive unit 4 via a drive coupling 26, where the drive coupling 26 is connecting the outgoing shaft of the drive unit 4 and the drive shaft 20 of the planetary drive system. The grinding unit 3 may be designed so that the drive shaft 20 of the planetary drive system 7 is passing through an opening 21 in the upper housing 5. If instead a gear unit is used for indirectly connecting the drive unit 4 to the planetary drive system 7, the gear unit may be provided with an outgoing shaft that is releasably connecting the gear unit to the planetary drive system 7. The drive coupling 26 may be of any suitable conventional type, where the outgoing shaft can be released from the planetary drive unit 7 when the lower housing 6 is removed from the upper housing 5, and again connected to the planetary drive unit 7 when the lower housing 6 is attached to the upper housing 5. With this arrangement, the drive shaft 20 of the planetary drive system 7 is releasably connected to the drive unit 4 via the drive coupling 26, and the drive shaft 20 is passing through the opening 21 in the upper housing 5.

The lower housing 6 may as shown in FIG. 2b be provided with a hollow shaft 42. The upper housing 5 is releasably connected to and held in position in relation to the lower housing 6 through the hollow shaft 42 and a first bearing unit 43 connected to the hollow shaft 42, where the first bearing unit 43 is rotatably connecting the hollow shaft 42 of the lower housing 6 and the upper housing 5. Through this configuration the lower housing 6 may be connected to a rotating part of the first bearing unit 43 and the upper housing 5 may be releasably connected to a non-rotating part of the first bearing unit 43. When the lower housing 6 is connected to the upper housing 5, the first bearing unit 43 secures that the lower housing 6 can rotate in relation to the upper housing 5. The first bearing unit 43 can for example be releasably connected to the upper housing 5 with bolt, screws or other suitable fastening means for easy maintenance or servicing of the grinding unit 3. Also the first bearing unit 43 has a hollow configuration so that the drive shaft 20 of the planetary drive system 7 can rotate in relation to the upper housing 5 and the lower housing 6. The drive shaft 20 may for example be attached to the lower housing 5 with a suitable second bearing unit 44. Depending on the design of the grinding unit 3, one or more further bearings may also be used for holding the drive shaft 20 in position in relation to other components of the grinding unit 3.

As shown in FIGS. 2b , 3 and 4 a-b, the planetary drive system 7 comprises a belt drive unit 25 arranged on the lower housing 6 and the belt drive unit 25 is connected to the drive unit 4. The belt drive unit 25 can be a conventional belt drive system and is arranged to rotate the lower housing 6 in relation to the upper housing 5, and also to rotate the one or more grinding disks 13 in relation to the lower housing 6. The belt drive unit 25 comprises a drive belt 29 that is connected to the drive shaft 20 and each of the one or more grinding disks 13 is connected to a pulley 30. The pulleys are arranged on the disk shafts 41 and a rotational movement is transferred from the drive unit 4 to the one or more grinding disks 13 via the drive shaft 20, the drive belt 29 and the one or more pulleys 30. When the outgoing shaft of the drive unit 4 is directly or indirectly connected to the drive shaft 20 of the planetary drive system 7 via the drive coupling 26, the drive shaft 20 can be rotatably driven by the drive unit 4. The rotational movement of the drive shaft 20 is transferred into a rotational movement of each of the disk shafts 41 via the drive belt 29 that is connected to each of the pulleys 30.

As schematically shown for example in FIG. 2b , the planetary drive system 7 further comprises a ring gear 27 arranged on the inner surface 16 a of the first side wall 9 of the upper housing 5. The ring gear 27 is interacting with at least one pinion 28 that is rotatably connected to the lower housing 6. The at least one pinion 28 is rotated by the belt drive unit 25. As shown in FIGS. 3 and 4 a-b, the pinions 28 are attached to the disk shafts 41 and the rotational movement of the drive shaft 20 is transferred to the disk shafts 41 and the pinions 28 via the drive belt 29 and the pulley 30 as described above. When the pulley 30 is rotated by the drive belt 29, also the pinions 28 are being rotated. Through the interaction between the at least one pinion 28 and the ring gear 27 the rotational movement of the at least one pinion 28 is transferred into to a rotational movement of the lower housing 6.

It should be noted that the planetary drive system may have other configurations that the one described above. The drive belt 29 may be of any suitable type and have an endless belt configuration, such as a toothed belt drive system or a traditional non-toothed belt drive system. The hollow shaft 42 may be provided with suitable openings for the drive belt 29. Instead of a drive belt system, a chain or other suitable drive means may be used. Further, it would be possible to design the drive system so that only one of the grinding disks 13 is directly driven by the drive belt 29 via only one of the disk shafts 41. The disk shafts 41 could then be connected to each other via a secondary drive system, where for example a second drive belt is used for connecting the disk shafts 41.

The grinding unit 3 may also be provided with other sealing members than the sealing element 18. As an example, the first bearing unit 43 may be sealed in relation to the upper housing 5 and the lower housing 6 to secure that contaminants are not entering the sealed volume 22.

The dimensions of the floor grinding machine 1 and the parts of the floor grinding machine 1 may be varied depending on the size and design of a specific grinding machine model. As a non-limiting example and depending on the design of the grinding unit 3, when viewed from above or below the upper housing 5 may have an outer diameter within the range 400-1200 mm, and the lower housing 6 may have an outer diameter within the range 400-1200 mm. The gap 15 formed in the radial direction R between the first side wall 9 and the second side wall 12, may as a non-limiting example have an extension in the radial direction within the range 5-40 mm, and thus the sealing element 18 may have a thickness in the radial direction R within the range 5-40 mm. Other dimensions are also possible. The gap 15 may have an extension in the radial direction R that varies in the axial direction AX, depending on the shapes of the first side wall 9 and the second side wall 12 respectively.

It will be appreciated that the above description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure as defined in the claims. Furthermore, modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out the teachings of the present disclosure, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims. Reference signs mentioned in the claims should not be seen as limiting the extent of the matter protected by the claims, and their sole function is to make claims easier to understand. 

What is claimed is:
 1. A floor grinding machine comprising a supporting frame, a grinding unit attached to the supporting frame, and a drive unit connected to the grinding unit, where the grinding unit comprises an upper housing, a lower housing rotatably arranged in relation to the upper housing, and a planetary drive system connected to the drive unit, where the upper housing comprises a top plate and a first side wall projecting downwards from the top plate in an axial direction (AX), wherein the lower housing comprises a bottom plate and a second side wall, where one or more grinding disks adapted for holding a tool are rotatably attached to the bottom plate, where the planetary drive system is arranged to rotate the lower housing and the one or more grinding disks respectively, where the first side wall is coaxially arranged in relation to the second side wall, and where the first side wall in the axial direction (AX) at least partly is overlapping the second side wall, and wherein a gap is formed in a radial direction (R) between the first side wall and the second side wall, and where a sealing element is arranged in the gap.
 2. A floor grinding machine according to claim 1, wherein the gap is formed in the radial direction (R) between an inner surface of the first side wall and an outer surface of the second side wall.
 3. A floor grinding machine according to claim 2, wherein the second side wall is projecting upwards and/or downwards from the bottom plate in the axial direction (AX), and where the gap is formed in the radial direction (R) between the inner surface of the first side wall and the outer surface of the second side wall.
 4. A f loor grinding machine according to claim 2, wherein the sealing element is arranged along peripheries of the inner surface and the outer surface respectively, and where an outer edge of the sealing element is attached to the inner surface of the first side wall, wherein the outer surface of the second side wall is slidably in contact with an inner edge of the sealing element.
 5. A floor grinding machine according claim 2, wherein the sealing element is releasably attached to the inner surface of the first side wall, and arranged to be adjustably positioned in the axial direction (AX) along the inner surface of the first side wall.
 6. A f loor grinding machine according to claim 2, wherein the inner surface of the first side wall has an essentially circular cross-sectional shape around an axis (A) extending in the axial direction (AX) and the outer surface of the second side wall has an essentially circular cross-sectional shape around the axis (A) extending in the axial direction (AX).
 7. A floor grinding machine according to claim 1, wherein the top plate and the first side wall of the upper housing are forming a first space, where the lower housing at least partly is arranged inside the first space of the upper housing
 8. A floor grinding machine according to claim 1, wherein the second side wall is projecting upwards from the bottom plate in the axial direction (AX), and where the gap is formed in the radial direction (R) between an inner surface of the second side wall and an outer surface of the first side wall.
 9. A floor grinding machine according to claim 8, wherein the inner surface of the second side wall has an essentially circular cross-sectional shape around an axis (A) extending in the axial direction (AX) and the outer surface of the first side wall has an essentially circular cross-sectional shape around the axis (A) extending in the axial direction (AX).
 10. A floor grinding machine according to claim 8, wherein the bottom plate and the second side wall of the lower housing are forming a second space (19), where the upper housing at least partly is arranged inside the second space (19) of the lower housing.
 11. A floor grinding machine according to claim 1, wherein the upper housing, the lower housing, and the sealing element are forming a sealed volume of the grinding unit (3), where the sealing element is preventing contaminants from entering the sealed volume.
 12. A floor grinding machine according to claim 1, wherein a drive shaft of the planetary drive system is releasably connected to the drive unit via a drive coupling, and where the drive shaft is passing through an opening in the upper housing.
 13. A floor grinding machine according to claim 1, wherein the planetary drive system comprises a belt drive unit arranged on the lower housing connected to the drive unit, where the belt drive unit is arranged to rotate the lower housing in relation to the upper housing, and to rotate the one or more grinding disks in relation to the lower housing.
 14. A floor grinding machine according to claim 13, wherein the belt drive unit comprises a drive belt, where each of the one or more grinding disks is connected to a pulley, where a rotational movement is transferred from the drive unit to the one or more grinding disks via the drive belt and the one or more pulleys.
 15. A floor grinding machine according to claim 13, wherein the planetary drive system comprises a ring gear arranged on an inner surface of the first side w all of the upper housing, where the ring gear is interacting with at least one pinion rotatably connected to the lower housing, and where the at least one pinion is rotated by the belt drive unit.
 16. A floor grinding machine according to claim 1, wherein the grinding unit is pivotally attached to the supporting frame about a lateral axis (L).
 17. A floor grinding machine according to claim 1, wherein the upper housing is non-rotatably arranged in relation to the supporting frame.
 18. A floor grinding machine according to claim 1, wherein the upper housing and/or the lower housing are made of ductile cast iron.
 19. A floor grinding machine according to claim 1, wherein the sealing element is a radial seal having a continuous configuration made of an elastomeric material, such as nitrile butadiene rubber (NBR) or carboxylated nitrile rubber (XNBR). 